The field of the invention is in the primary battery art, and more particularly in the art of porous electrode primary batteries.
In the absence of good history records, it has been quite difficult to determine the present condition of a primary battery with respect to its remaining useful life. Generally, the voltage and current characteristics of a battery with, for example, half its useful life used up are substantially the same as a new battery. With secondary batteries, which can be recharged, the necessity of knowing their state of charge is generally not so important as they can be readily recharged to substantially a known energy content.
The best known prior art is that of U.S. Pat. Nos. 2,988,590 to patentee H. G. Andre, and 3,720,869 to patentee Rowlette.